In a 3rd generation telecommunication system including the feature of High-Speed Downlink Packet Access (HSDPA), e.g. as described in the document 3GPP TR 25.848: “Physical Layer Aspects of UTRA High Speed Downlink Packet Access” issued by the 3rd Generation Partnership Project (3GPP), each user equipment (UE) is allocated a dedicated channel (DPCH) in both directions to exchange higher layer signalling information for example between user equipment and Radio Network Controller (RNC).
In order to handle high loads in a cell for example due to a large number of
HSDPA users in said cell, the concept of a Fractional Dedicated Physical Channel (F-DPCH) has been introduced in release 6 of the 3GPP specifications for 3rd generation telecommunication systems. The F-DPCH is arranged to carry TPC (Transmit Power Control) commands of several HSDPA users for power control. The channels for TPC commands for the users are time multiplexed in the F-DPCH. The corresponding signalling radio bearers (SRB) arranged to carry radio resource control (RRC) related information when using F-DPCH, are mapped on a High Speed Downlink Shared Channel (HS-DSCH). The radio resource control (RRC) related information relates for example to cell change, active set update, RB reconfiguration, etc.
As is understood from the above, the signalling bearers are sent to the user equipment on the High Speed Downlink Shared Channel (HS-DSCH) when F-DPCH is used. However, this channel does not support soft handover. This can in some cases lead to the situation that the signalling radio bearer can be lost due to poor HS-DSCH reception quality at the user equipment. The uplink quality, e.g. for the UL SRB:s, on the other hand, can still be sufficient since both DCH and E-DCH can gain from the benefits of the soft handover operation. As mentioned above, the signalling radio bearers (SRB) can carry vital radio resource control (RRC) related information such as active set update, cell change, radio bearer reconfiguration etc (see for example the document 3GPP TS25.311: “Radio Resource Control Protocol Specification (FDD)”). This means that the loss of a downlink signalling radio bearer (SRB) can lead to unnecessary SRB retransmissions, call drops, loss of handover commands, and increased delay in scheduling the user in a new HS-DSCH serving cell.
WO 2007/025971 discloses a method for executing handover, wherein radio resource messages are bi-casted through both current serving cell and target cell during handover.